This invention relates to an antibacterial glass for use as a resin-filling antibacterial agent and to a resin composite comprising a resin and the antibacterial glass.
A resin product such as a toothbrush, a soap case, a washbowl, a washstand, or a bathtub is used under a high-humidity condition and therefore suffers easy growth of bacteria and mold. In order to suppress the growth of bacteria and mold, use has been made of an antibacterial agent which is mixed with a resin. Generally, the antibacterial agent utilizes silver oxide which has an excellent antibacterial function. For example, zeolite powder containing silver ions in the crystal structure and soluble glass powder containing AgO as a glass composition are known as the antibacterial agent. However, silver oxide is expensive and the amount to be used is sometimes restricted due to economical reasons. On the other hand, the soluble glass powder containing AgO tends to be discolored under the effect of ultraviolet rays and heat during long-time use and is therefore unfavorable. Such discoloration is particularly undesirable if the resin product. has a white color.
In view of the above, it is proposed to use a ZnO-based glass as the antibacterial agent. The ZnO-based glass is inexpensive and is never discolored under the effect of ultraviolet rays and heat. For example, Japanese Unexamined Patent Publication (JP-A) No. H07-257938 (257938/1995) discloses antibacterial glass powder comprising a ZnOxe2x80x94B2O3xe2x80x94Na2O glass.
However, if a resin product comprises a resin filled with the above-mentioned glass powder containing ZnO, several problems in appearance will arise during use of the resin product. Specifically, with lapse of time, the resin product loses the brightness to become dull in appearance. In addition, a rough touch is produced on the surface of the resin product.
It is an object of this invention to provide an antibacterial glass which contains ZnO but will not adversely affect the appearance of a resin product comprising a resin and the antibacterial glass mixed therewith.
It is another object of this invention to provide a resin composite including the above-mentioned antibacterial glass.
According to this invention, there is provided an antibacterial glass which is a ZnOxe2x80x94B2O3xe2x80x94SiO2 glass and which includes 0-6 wt % Na2O.
According to this invention, there is also provided a resin composite comprising a resin and an antibacterial agent. The antibacterial agent comprises an antibacterial glass which is a ZnOxe2x80x94B2O3xe2x80x94SiO2 glass and which contains 0-6 wt % Na2O.
An antibacterial glass according to this invention comprises a ZnOxe2x80x94B2O3xe2x80x94SiO2 glass. This is because the ZnOxe2x80x94B2O3xe2x80x94SiO2 glass has an appropriate solubility so that ZnO is released as Zn2+ ions to provide an antibacterial function to a resin. Thus, ZnO is a primary factor providing the antibacterial function and is therefore an essential component. B2O3 and SiO2 are glass-forming oxides which are essential to obtain the glass containing ZnO and having the appropriate solubility. It is important in this invention to restrict the content of a sodium component in the glass, i.e., to 6 wt % or less in terms of Na2O. If the content of Na2O exceeds 6 wt %, the resin product loses its brightness during long-time use.
The antibacterial glass may have various composition ranges as far as the above-mentioned condition is satisfied. Preferably, the antibacterial glass consists essentially of, by weight percent, 55-65% ZnO, 18-30% B2O3, 8-20% SiO2, 0-10% MgO, and 0-6% Na2O.
The reason why the composition range is defined as mentioned above is as follows.
The content of ZnO is 55-65 wt %, preferably, 55-60 wt %. If the content of ZnO is less than 55 wt %, the antibacterial effect is decreased. On the other hand, if the content exceeds 60 wt %, vitrification is difficult.
The content of B2O3 is 18-30 wt %, preferably, 20-25 wt %. If the content of B2O3 is less than 20 wt %, vitrification tends to become difficult. If the content is less than 18 wt %, vitrification is difficult. On the other hand, if the content exceeds 25 wt %, the water-resistance of the glass tends to be degraded. If the content exceeds 30 wt %, the water-resistance is drastically degraded so that the release of Zn2+ ions exceeds an appropriate level. As a result, the antibacterial function can not be maintained for a long period of time. This unfavorably shortens the life of the antibacterial glass.
SiO2 is a glass-forming component. The content of SiO2 is 8-20 wt %, preferably, 10-15 wt %. If the content of SiO2 is less than 10 wt %, vitrification tends to become difficult. If the content is less than 8 wt %, vitrification is difficult. On the other hand, if the content exceeds 15 wt %, the release of Zn2+ ions from the glass tends to be decreased. If the content exceeds 20 wt %, the release of Zn2+ ions from the glass is considerably decreased so that the antibacterial function is insufficient.
MgO has an effect of lowering the viscosity of the glass and acts like a flux which promotes the melting of the glass. The content of MgO is 0-10 wt %, preferably, 3-7 wt %. MgO need not essentially be contained but is preferably contained in an amount of 3 wt % or more in order to assure stable melting of the glass. However, if the content exceeds 7 wt %, the appearance of the resin product tends to be affected. If the content exceeds 10 wt %, the resin product will lose its brightness during long-time use Na2O can be added up to 6 wt %, preferably, up to 4 wt %, more preferably, up to 0.5 wt % or less in order to improve the meltability of the glass. However, since the influence upon the appearance of the resin product is great as mentioned above, it is desired not to contain Na2O.
Furthermore, other components may be added as far as the characteristics of the glass such as the chemical durability, the solubility, and the antibacterial function are not adversely affected. For example, CaO, SrO, BaO, Li2O, K2O, Al2O3, TiO2, and ZrO2 can be added.
The antibacterial glass of this invention can be provided in various forms such as glass powder, glass fiber, and glass flakes. Among others, the glass powder achieves a good antibacterial function because a specific surface area is larger than fiber and flakes. The average particle size of the glass powder is between 1 and 20 xcexcm, preferably, between 2 and 20 xcexcm. Specifically, if the average particle size of the glass powder is smaller than 1 xcexcm, it is difficult to mix the glass powder with the resin. If the average particle size is larger than 20 xcexcm, the release of Zn2+ ions per unit weight is unfavorably reduced.
The antibacterial glass of this invention can be used as an antibacterial agent to be filled into thermosetting resin or thermoplastic resin. For example, it is possible to use the antibacterial glass with phenol resin, polyester resin, melamine resin, urea resin, diallylphthalate resin, epoxy resin, silicone resin, vinyl chloride resin, vinyl acetate resin, polyethylene resin, polystyrene resin, polypropylene resin, acrylic resin, polyurethane resin, SAN (styrene acrylonitrile) resin, ABS (acrylonitrile butadiene styrene) resin, polycarbonate resin, fluororesin, polyimide resin, polyphenyl sulfide resin, and a composite thereof. Among others, use is preferably made of acrylic resin, polyester resin, melamine resin, and ABS resin typically used in sanitary containers and silicone resin typically used as a sealing material.
The antibacterial glass of this invention is not only applicable to the resin-filling antibacterial agent but also used in various antibacterial applications such as an antibacterial enamel to cover a glass or ceramics and an antibacterial paint to cover a metal.
A resin composite according to this invention contains the above-mentioned antibacterial glass. The content of the antibacterial glass is 0.1-70 vol %, preferably, 0.1-10 vol %. The reason why the content is restricted as mentioned above is as follows. If the content is less than 0.1 vol %, it is difficult to provide a sufficient antibacterial function to the resin product. On the other hand, the antibacterial effect is increased as the content of the antibacterial glass is greater. However, the antibacterial effect is no longer increased if the content exceeds 10 vol %. If the content exceeds 70 vol %, molding of the resin becomes difficult.
As the resin, use may be made of phenol resin, polyester resin, melamine resin, urea resin, diallylphthalate resin, epoxy resin, silicone resin, vinyl chloride resin, vinyl acetate resin, polyethylene resin, polystyrene resin, polypropylene resin, acrylic resin, polyurethane resin, SAN (styrene acrylonitrile) resin, ABS (acrylonitrile butadiene styrene) resin, polycarbonate resin, fluororesin, polyimide resin, polyphenyl sulfide resin, and a composite thereof. Among others, use is preferably made of acrylic resin, polyester resin, melamine resin, and ABS resin typically used in sanitary containers and silicone resin typically used as a sealing.
In the resin composite of this invention, various additives typically contained in the resin product or another antibacterial agent may be appropriately contained in addition to the antibacterial glass.